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- Kernel driver ds1621
- ====================
- Supported chips:
- * Dallas Semiconductor DS1621
- Prefix: 'ds1621'
- Addresses scanned: I2C 0x48 - 0x4f
- Datasheet: Publicly available at the Dallas Semiconductor website
- http://www.dalsemi.com/
- * Dallas Semiconductor DS1625
- Prefix: 'ds1621'
- Addresses scanned: I2C 0x48 - 0x4f
- Datasheet: Publicly available at the Dallas Semiconductor website
- http://www.dalsemi.com/
- Authors:
- Christian W. Zuckschwerdt <zany@triq.net>
- valuable contributions by Jan M. Sendler <sendler@sendler.de>
- ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
- with the help of Jean Delvare <khali@linux-fr.org>
- Module Parameters
- ------------------
- * polarity int
- Output's polarity: 0 = active high, 1 = active low
- Description
- -----------
- The DS1621 is a (one instance) digital thermometer and thermostat. It has
- both high and low temperature limits which can be user defined (i.e.
- programmed into non-volatile on-chip registers). Temperature range is -55
- degree Celsius to +125 in 0.5 increments. You may convert this into a
- Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
- parameter is not provided, original value is used.
- As for the thermostat, behavior can also be programmed using the polarity
- toggle. On the one hand ("heater"), the thermostat output of the chip,
- Tout, will trigger when the low limit temperature is met or underrun and
- stays high until the high limit is met or exceeded. On the other hand
- ("cooler"), vice versa. That way "heater" equals "active low", whereas
- "conditioner" equals "active high". Please note that the DS1621 data sheet
- is somewhat misleading in this point since setting the polarity bit does
- not simply invert Tout.
- A second thing is that, during extensive testing, Tout showed a tolerance
- of up to +/- 0.5 degrees even when compared against precise temperature
- readings. Be sure to have a high vs. low temperature limit gap of al least
- 1.0 degree Celsius to avoid Tout "bouncing", though!
- The alarm bits are set when the high or low limits are met or exceeded and
- are reset by the module as soon as the respective temperature ranges are
- left.
- The alarm registers are in no way suitable to find out about the actual
- status of Tout. They will only tell you about its history, whether or not
- any of the limits have ever been met or exceeded since last power-up or
- reset. Be aware: When testing, it showed that the status of Tout can change
- with neither of the alarms set.
- Temperature conversion of the DS1621 takes up to 1000ms; internal access to
- non-volatile registers may last for 10ms or below.
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